Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. It is used in a wide variety of commercial and military electronic devices and equipment. To store information, flash memory includes an addressable array of memory cells, typically made from floating gate transistors. Common types of flash memory cells include stacked gate memory cells and split gate flash memory cells. Split gate flash memory cells are semiconductor devices, typically formed as part of integrated circuits. Recently, split gate flash memory cells have received great attention due to the development of high memory capacities (relative to other types of flash memory cells). Split gate flash memory cells have several advantages over stacked gate memory cells, such as lower power consumption, higher injection efficiency, less susceptibility to short channel effects, and over erase immunity.
However, when a bottom anti-reflection coating (BARC) layer includes a low-viscosity material, the BARC layer has a thinner thickness near an edge of a functional area. An external surface of the BARC layer overlying various features shows a steep slope from a central portion to the edge of the functional area, so that the external surface cannot be parallel to the top surface of the underlying features along a horizontal dot-line. The uneven thickness of the BARC layer causes the overlying control gates near the edge of the functional area to slide down, resulting in worse critical dimension uniformity (CDU) within the functional area.